U.S. patent application number 14/104557 was filed with the patent office on 2014-06-12 for developing device and image forming apparatus.
This patent application is currently assigned to Konica Minolta, Inc.. The applicant listed for this patent is Konica Minolta, Inc.. Invention is credited to Tatsuya FURUTA, Kazuteru ISHIZUKA, Seiko ITAGAKI, Tomohiro KAWASAKI, Kazuhiro SAITO.
Application Number | 20140161472 14/104557 |
Document ID | / |
Family ID | 50881083 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140161472 |
Kind Code |
A1 |
SAITO; Kazuhiro ; et
al. |
June 12, 2014 |
DEVELOPING DEVICE AND IMAGE FORMING APPARATUS
Abstract
Disclosed herein is a developing device including: a developer
housing section configured to house a developer including toner and
carrier; a carrier replenishing section configured to supply the
carrier to the developer housing section; a carrier concentration
detecting section provided at a position near a carrier
replenishment position at which the carrier is received from the
carrier replenishing section in the developer housing section, the
carrier concentration detecting section being configured to detect
a carrier concentration in the developer housing section; and a
carrier replenishment determination section configured to determine
whether the carrier is properly supplied to the developer housing
section on the basis of a result of detecting by the carrier
concentration detecting section.
Inventors: |
SAITO; Kazuhiro; (Tokyo,
JP) ; KAWASAKI; Tomohiro; (Kanagawa, JP) ;
ISHIZUKA; Kazuteru; (Saitama, JP) ; FURUTA;
Tatsuya; (Tokyo, JP) ; ITAGAKI; Seiko; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Konica Minolta, Inc. |
Tokyo |
|
JP |
|
|
Assignee: |
Konica Minolta, Inc.
Tokyo
JP
|
Family ID: |
50881083 |
Appl. No.: |
14/104557 |
Filed: |
December 12, 2013 |
Current U.S.
Class: |
399/27 |
Current CPC
Class: |
G03G 15/5058 20130101;
G03G 15/0856 20130101; G03G 2215/0132 20130101; G03G 2215/0164
20130101; G03G 15/0849 20130101 |
Class at
Publication: |
399/27 |
International
Class: |
G03G 15/08 20060101
G03G015/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2012 |
JP |
2012-271297 |
Claims
1. A developing device comprising: a developer housing section
configured to house a developer including toner and carrier; a
carrier replenishing section configured to supply the carrier to
the developer housing section; a carrier concentration detecting
section provided at a position near a carrier replenishment
position at which the carrier is received from the carrier
replenishing section in the developer housing section, the carrier
concentration detecting section being configured to detect a
carrier concentration in the developer housing section; and a
carrier replenishment determination section configured to determine
whether the carrier is properly supplied to the developer housing
section on the basis of a result of detecting by the carrier
concentration detecting section.
2. The developing device according to claim 1, wherein the carrier
concentration detecting section measures a magnetic permeability of
the developer in the developer housing section to detect the
carrier concentration.
3. The developing device according to claim 1, wherein the carrier
replenishment determination section determines that the carrier is
properly supplied to the developer housing section when a carrier
concentration detected by the carrier concentration detecting
section is not lower than a predetermined concentration, and
determines that the carrier is not properly supplied to the
developer housing section when the carrier concentration detected
by the carrier concentration detecting section is lower than the
predetermined concentration.
4. The developing device according to claim 1, wherein the carrier
replenishment determination section determines whether the carrier
is properly supplied to the developer housing section on the basis
of a result of detecting by the carrier concentration detecting
section in a period from a start of supply of the carrier by the
carrier replenishing section until the carrier exits a detecting
region of the carrier concentration detecting section.
5. The developing device according to claim 1, wherein the carrier
replenishment determination section determines whether the carrier
is properly supplied to the developer housing section on the basis
of a result of detecting by the carrier concentration detecting
section in a period from a time when the carrier starts to pass
through a detecting region of the carrier concentration detecting
section until the carrier exits the detecting region, after supply
of the carrier by the carrier replenishing section is started.
6. The developing device according to claim 1 further comprising a
notification section configured to indicate a result of
determination by the carrier replenishment determination section
when the carrier replenishment determination section determines
that the carrier is not properly supplied to the developer housing
section.
7. An image forming apparatus comprising the developing device
according to claim 1.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is entitled and claims the benefit of
Japanese Patent Application No. 2012-271297, filed on Dec. 12,
2012, the disclosure of which including the specification, drawings
and abstract is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a developing device and an
image forming apparatus.
[0004] 2. Description of Related Art
[0005] Conventionally, one-component development methods and
two-component development methods are employed in
electrophotographic developing devices. In one-component
development methods, toner makes contact with each member of a
developing device at a part for supplying toner, a part for
charging toner, a part for neutralizing toner, and a part for
collecting toner, and as a result stress is applied to the toner.
Thermoplastic resins are used to form a toner, and inorganic fine
particles serving as a flowability modifier are attached on the
surface of the toner. Therefore, due to the above-mentioned stress,
thermal variation may be caused and the inorganic fine particles
may be buried in the toner surface. In the case of high-speed
apparatuses, the stress applied to toner is even greater since the
rotational speed of each component thereof is high. For this
reason, the speed is limited. In addition, in recent years, the
particle size of toner is remarkably reduced as the image quality
is enhanced, and a toner having the diameter of 6 [.mu.m] or less
is not uncommon. Since such a small-sized toner is treated with
many post-treatment materials and its fluidity is degraded, the
aggregation of the toner and burying of the post-treatment
materials due to the above-mentioned stress frequently occur. In
addition, there has been a growing trend toward low-temperature
fixation in view of environmental considerations. This trend
results in decreased thermotolerance, which is disadvantageous in
terms of the above-mentioned stress.
[0006] In two-component development methods, toner charged by
triboelectric charging of the toner and carrier is attached to an
electrostatic latent image formed on an image bearing member to
thereby develop the image. In a developing device, the ratio of the
toner and carrier is kept at a certain ratio to maintain the
charging state of the toner. However, when a toner image is
developed on the electrostatic latent image formed on the image
bearing member, the toner becomes insufficient. Therefore, toner is
supplied by replenishing means. The toner supplied by the
replenishing means is uncharged toner, which is charged when it is
stirred with a developer in a developing device by stirring means
in the developing device, and conveyed by conveying means in the
developing device. Since in such a method charging is performed by
mixing particles, the stress applied to toner is small.
Accordingly, in comparison with the case of one-component
development methods, the toner has a longer life, and besides, has
greater adaptability to high speed. Since the surface area of the
carrier is greater than that of the toner, the carrier is less
likely to be contaminated by the toner adhered to the surface of
the carrier. However, after a long period of use, contamination
(spent) on the surface of the carrier increases, and thus the
performance for charging toner decreases with time. As a result,
problems such as fogging and toner scattering occur. In order to
extend the life of two-component developing devices, it is
conceivable to increase the amount of carrier housed in the
developing device. In that case, however, the size of the
developing device is increased, which is undesirable.
[0007] To solve the above-mentioned problems of two-component
developers, Japanese Examined Patent Publication No. 2-21591
discloses a developing device of a trickle type in which a
developer is supplied to the developing device little by little,
and a developer whose charging performance is degraded is
discharged from the developing device little by little, to thereby
suppress the increase of degraded carrier. This developing device
utilizes change in volume of the developer to discharge the excess
and degraded developer so as to maintain a substantially constant
volume level of the developer in the developing device. With this
developing device of the trickle type, the degraded carrier in the
developing device is replaced by newly supplied carrier, and the
charging performance of the carrier in the developing device can be
maintained at a substantially constant level.
[0008] A device of a trickle type has been conceived in which, for
the purpose of simplifying the configuration of the device, toner
and carrier are supplied from a developer cartridge that houses a
developer obtained by mixing the toner and carrier at a constant
ratio so as to simultaneously supply the toner and carrier.
However, a toner consumption amount per one recording sheet
(hereinafter referred to simply as "toner consumption amount")
differs greatly depending on the image to be formed. For example, a
document with only letters tends to consume a small amount of toner
while a photographic image tends to consume a large amount of
toner. On the other hand, degradation of carrier depends on the
number of stirring carried out in the developing device, in other
words, the number of image formation (the number of recording
sheets), not on the toner consumption amount.
[0009] Therefore, when the developer obtained by mixing the toner
and carrier at a constant ratio is supplied in accordance with the
toner consumption amount, then a large amount of toner has to be
supplied in the case where the toner consumption amount is large,
and as a result, carrier is unnecessarily supplied and wastefully
discarded. Conversely, in the case where the toner consumption
amount is small, it is not necessary to supply a large amount of
toner, and therefore, the amount of carrier to be supplied is
decreased, and, so to speak, the metabolism of the carrier is
deteriorated, which may degrade the charging performance. For this
reason, techniques are proposed in which toner and carrier are not
previously mixed, but are separately supplied (see, for example,
Japanese Patent Application Laid-Open No. 2001-183893, and Japanese
Patent No. 2986001).
[0010] In the technique according to Japanese Patent Application
Laid-Open No. 2001-183893, a toner concentration detector that
stably detects the toner concentration (the ratio of toner in the
developer) in a steady state in a developing device is provided at
a position where supplied toner and carrier are sufficiently mixed
with a developer in the developing device. When the toner
concentration detected by the toner concentration detector is lower
than a previously set toner concentration, toner replenishment is
performed for the toner consumed by the development. When the toner
concentration detected by the toner concentration detector is not
reset to a predetermined value, or is further decreased after the
toner replenishment, a warning message is displayed on a monitor,
for example. In this manner, a user can recognize that the toner
replenishment has not been properly performed, and can recognize
the necessity of measures such as reconditioning of a toner
replenishment mechanism and replacement of a toner bottle that is
provided above a toner hopper and configured to supply toner to the
toner hopper.
[0011] On the other hand, when an error occurs in a carrier
replenishment mechanism or when the carrier hopper is empty, the
carrier replenishment is not properly performed. Since carrier in
the developing device is not typically consumed, however, the toner
concentration detected by the toner concentration detector does not
change, and thus the user cannot recognize the fact that the
carrier replenishment has not been properly performed. In an early
stage, a carrier replenishment failure has no influence on formed
images and raises no problem. However, since degraded carrier is
not replaced with newly supplied carrier, degradation of carrier is
gradually facilitated, and accordingly the toner charging
performance is degraded with time. As a result, the problems such
as fogging and toner scattering occur.
[0012] It is to be noted that, while Japanese Patent No. 2986001
discloses a technique in which the toner concentration in a
developing device and the amount of discharged developer are
detected, whether the carrier replenishment has been properly
performed cannot be recognized since the developer to be discharged
is strongly influenced by factors (such as inclination of the
developing device and change in volume of the developer due to
environmental changes) other than the carrier replenishment.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a
developing device and an image forming apparatus which can prevent
problems which are caused when supply of carrier has not been
properly performed in the case where toner and carrier are
separately supplied.
[0014] To achieve the abovementioned object, a developing device
reflecting one aspect of the present invention includes a developer
housing section configured to house a developer including toner and
carrier; a carrier replenishing section configured to supply the
carrier to the developer housing section; a carrier concentration
detecting section provided at a position near a carrier
replenishment position at which the carrier is received from the
carrier replenishing section in the developer housing section, the
carrier concentration detecting section being configured to detect
a carrier concentration in the developer housing section; and a
carrier replenishment determination section configured to determine
whether the carrier is properly supplied to the developer housing
section on the basis of a result of detecting by the carrier
concentration detecting section.
[0015] Desirably, in the above-mentioned developing device, the
carrier concentration detecting section measures a magnetic
permeability of the developer in the developer housing section to
detect the carrier concentration.
[0016] Desirably, in the above-mentioned developing device, the
carrier replenishment determination section determines that the
carrier is properly supplied to the developer housing section when
a carrier concentration detected by the carrier concentration
detecting section is not lower than a predetermined concentration,
and determines that the carrier is not properly supplied to the
developer housing section when the carrier concentration detected
by the carrier concentration detecting section is lower than the
predetermined concentration.
[0017] Desirably, in the above-mentioned developing device, the
carrier replenishment determination section determines whether the
carrier is properly supplied to the developer housing section on
the basis of a result of detecting by the carrier concentration
detecting section in a period from a start of supply of the carrier
by the carrier replenishing section until the carrier exits a
detecting region of the carrier concentration detecting
section.
[0018] Desirably, in the above-mentioned developing device, the
carrier replenishment determination section determines whether the
carrier is properly supplied to the developer housing section on
the basis of a result of detecting by the carrier concentration
detecting section in a period from a time when the carrier starts
to pass through a detecting region of the carrier concentration
detecting section until the carrier exits the detecting region,
after supply of the carrier by the carrier replenishing section is
started.
[0019] Desirably, the above-mentioned developing device further
includes a notification section configured to indicate a result of
determination by the carrier replenishment determination section
when the carrier replenishment determination section determines
that the carrier is not properly supplied to the developer housing
section.
[0020] An image forming apparatus reflecting another aspect of the
present invention includes the above-mentioned developing
device.
BRIEF DESCRIPTION OF DRAWINGS
[0021] The present invention will become more fully understood from
the detailed description given hereinbelow and the appended
drawings which are given by way of illustration only, and thus are
not intended as a definition of the limits of the present
invention, and wherein:
[0022] FIG. 1 is a vertical sectional view of an image forming
apparatus according to the present embodiment;
[0023] FIG. 2 is a control block diagram of the image forming
apparatus according to the present embodiment;
[0024] FIG. 3 illustrates a configuration of a developing device
according to the present embodiment;
[0025] FIG. 4 is a flowchart illustrating a toner replenishment
control operation according to the present embodiment;
[0026] FIG. 5 is a flowchart illustrating the operation for
checking toner replenishment according to the present
embodiment;
[0027] FIG. 6 is a flowchart illustrating a carrier replenishment
control operation according to the present embodiment;
[0028] FIG. 7 illustrates a change of a carrier concentration
detected by a carrier concentration detector according to the
present embodiment;
[0029] FIG. 8 illustrates a configuration of a developing device
according to a comparative configuration of the present embodiment;
and
[0030] FIG. 9 illustrates a change of a carrier concentration
detected by a carrier concentration detector according to the
comparative configuration of the present embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] In the following, the present embodiment is described in
detail with reference to the drawings.
[Configuration of Image Forming Apparatus 1]
[0032] Image forming apparatus 1 illustrated in FIGS. 1 and 2 is a
color image forming apparatus with an intermediate transfer system
using electrophotographic process technology. That is, image
forming apparatus 1 transfers (primarily transfers) respective
toner images of yellow (Y), magenta (M), cyan (C), and black (K)
formed on photoconductor drums 413 to intermediate transfer belt
421, and superimposes the toner images of the four colors on one
another on intermediate transfer belt 421. Then, image forming
apparatus 1 transfers (secondarily transfers) the resultant image
to sheet S, to thereby form an image.
[0033] A tandem system is adopted for image forming apparatus 1. In
the tandem system, respective photoconductor drums 413
corresponding to the four colors of YMCK are placed in series in
the miming direction of intermediate transfer belt 421, and the
toner images of the four colors are sequentially transferred to
intermediate transfer belt 421 in one cycle.
[0034] As illustrated in FIGS. 1 and 2, image forming apparatus 1
includes image reading section 10, operation/display section 20,
image processing section 30, image forming section 40, sheet
conveying section 50, fixing section 60, and control section 70.
Control section 70 functions as a carrier replenishment
determination section.
[0035] Control section 70 includes central processing unit (CPU)
71, read only memory (ROM) 72, and random access memory (RAM) 73.
CPU 71 reads a program suited to processing details out of ROM 72,
develops the program in RAM 73, and controls an operation of each
block of image forming apparatus 1 in cooperation with the
developed program. At this time, CPU 71 refers to various pieces of
data stored in storage section 82. Storage section 82 is composed
of, for example, a non-volatile semiconductor memory (so-called
flash memory) or a hard disk drive.
[0036] Control section 70 transmits and receives various data to
and from an external apparatus (for example, a personal computer)
connected to a communication network such as a local area network
(LAN) or a wide area network (WAN), through communication section
81. Control section 70 receives, for example, image data
transmitted from the external apparatus, and performs control to
form an image on a recording sheet on the basis of the image data
(input image data). Communication section 81 is composed of, for
example, a communication control card such as a LAN card.
[0037] Image reading section 10 includes auto document feeder (ADF)
11, document image scanner 12, and the like. Auto document feeder
11 causes a conveyance mechanism to feed document D placed on a
document tray, and sends out document D to document image scanner
12. Auto document feeder 11 can successively read images of
documents D placed on the document tray.
[0038] Document image scanner 12 optically scans a document fed
from auto document feeder 11 to its contact glass or a document
placed on its contact glass, and brings light reflected from the
document into an image on the light receiving surface of charge
coupled device (CCD) detector 12a, to thereby read the document
image. Image reading section 10 generates input image data on the
basis of reading results provided by document image scanner 12.
Image processing section 30 performs predetermined image processing
on the input image data.
[0039] Operation/display section 20 includes, for example, a liquid
crystal display (LCD) with a touch panel, and functions as display
section 21 and operation section 22. Display section 21 displays
various operation screens, image statuses, the operating conditions
of each function, and the like in accordance with display control
signals received from control section 100. Display section 21
functions as a notification section.
[0040] Operation section 22 includes various operation keys such as
a numeric keypad and a start key. Operation section 22 receives
various inputting operations performed by a user, and outputs
operation signals corresponding to the inputting operations to
control section 70. It is to be noted that the operation signals
may be output from external apparatuses to control section 70 via
communication section 81.
[0041] Image processing section 30 includes a circuit that performs
digital image processing suited to initial settings or user
settings, on the input image data, and the like. In addition, image
processing section 30 performs, on input image data, tone
correction, various kinds of correction processes such as color
correction, or a compression process, and the like. Image forming
section 40 is controlled on the basis of image data subjected to
such processes.
[0042] Image forming section 40 includes: image forming units 41Y,
41M, 41C, and 41K for images of color toners respectively
containing a Y component, an M component, a C component, and a K
component on the basis of the input image data; intermediate
transfer unit 42; and toner concentration detector 43, and the
like.
[0043] Image forming units 41Y, 41M, 41C, and 41K for the Y
component, the M component, the C component, and the K component
have the same configuration except for the color to be used. For
ease of illustration and description, common elements are denoted
by the same reference signs. Only when elements need to be
discriminated from one another, Y, M, C, or K is added to their
reference signs. In FIG. 1, reference signs are given to only the
elements of image forming unit 41Y for the Y component, and
reference signs are omitted for the elements of other image forming
units 41M, 41C, and 41K.
[0044] Next, the configuration of image forming unit 41 will be
described taking image forming unit 41Y as an example. Image
forming unit 41Y includes exposing device 411, developing device
412, photoconductor drum 413 (image bearing member), charging
device 414, cleaning device 415, and the like.
[0045] Photoconductor drum 413 is, for example, a negative charge
type organic photoconductor (OPC) formed by sequentially stacking
an under coat layer (UCL), a charge generation layer (CGL), a
charge transport layer (CTL), and an over coat layer (OCL) on the
circumferential surface of a conductive cylindrical body
(elementary tube) made of aluminum. It is to be noted that
photoconductor drum 413 may also be a photoconductor having a belt
form, not a roller form.
[0046] Charging device 414 negatively charges the entire surface of
photoconductor drum 413. Charging device 414 may be of any of a
contacting roller charging type, and a non-contacting corona
charging type.
[0047] Exposure device 411 is composed of, for example, a
semiconductor laser, and irradiates photoconductor drum 413 with
laser light corresponding to the image of the Y component. Because
the positive charge is generated in the charge generation layer of
photoconductor drum 413 and is transported to the surface of the
charge transport layer, the surface charge (negative charge) of
photoconductor drum 413 is neutralized. An electrostatic latent
image of the Y component is formed on the surface of photoconductor
drum 413 due to a difference in potential from its
surroundings.
[0048] Developing device 412 houses a developer of the Y-component.
The developer is a two-component developer composed of carrier and
toner having small particle size. As illustrated in FIG. 3,
developing device 412 drives developing roller 108 into rotation to
attach the toner of the Y-component to the surface of
photoconductor drum 413. Thus, developing device 412 visualizes the
electrostatic latent image to form a toner image.
[0049] Toner particles used in developing device 412 are typically
granulated by mixing, in a binder resin, a colorant, and as
necessary, a charge control agent, a releasing agent and the like
so as to have a predetermined particle size. Thereafter, the
particles thus granulated are coated with an external additive so
as to have a particle size of about 3 to 15 [.mu.m]. For the
granulation of toner particles, publicly known methods such as
pulverization methods, emulsion polymerization methods, and
suspension polymerization methods may be employed.
[0050] Drum cleaning device 415 includes a drum cleaning blade that
is brought into sliding contact with the surface of photoconductor
drum 413. Residual toner that remains on the surface of
photoconductor drum 413 after the primary transfer is removed by
the drum cleaning blade. It is to be noted that cleaning device 415
may be a cleaner of a multiple cleaning type which is a combination
of a cleaning brush, a cleaning roller, and other members.
Alternatively, it is possible to adopt a cleaner less type in which
developing device 412 corrects the residual toner after transfer,
without providing cleaning device 415.
[0051] Intermediate transfer unit 42 includes intermediate transfer
belt 421 serving as an intermediate transfer member, primary
transfer roller 422, secondary transfer roller 423, drive roller
424, driven roller 425, cleaning device 426 and the like.
[0052] Intermediate transfer belt 421 is composed of an endless
belt, and installed around drive roller 424 and driven roller 425
in a stretched state. Along with the rotation of drive roller 424
transfer belt 421 runs at a constant speed in the arrow A
direction. Intermediate transfer belt 421 is brought into pressure
contact with photoconductor drums 413 by primary transfer rollers
422, whereby the toner images of the four colors are
primary-transferred to intermediate transfer belt 421 so as to be
sequentially superimposed on each other. Then, intermediate
transfer belt 421 is brought into pressure contact with recording
sheet S by secondary transfer roller 423, whereby the toner image
primary-transferred on intermediate transfer belt 421 is
secondary-transferred to recording sheet S. It is to be noted that
a transfer charger, a transfer roller, and the like may be used as
the transferring member in place of the transferring system using
intermediate transfer belt 421. A direct transferring system in
which toner image is directly transferred from photoconductor drum
413 to recording sheet S may also be adopted.
[0053] Belt cleaning device 426 includes a belt cleaning blade that
is brought into sliding contact with the surface of intermediate
transfer belt 421. Residual toner that remains on the surface of
intermediate transfer belt 421 after secondary transfer is scraped
and removed by the belt cleaning blade. It is to be noted that
cleaning device 426 may be a cleaner of a multiple cleaning type
which is a combination of a cleaning brush, a cleaning roller, and
other members.
[0054] As illustrated in FIG. 1, toner concentration detector 43 is
disposed on the downstream side in the rotational direction of
intermediate transfer belt 421 relative to a secondary transfer
position where toner images are secondary-transferred to recording
sheet S, in facing relation to intermediate transfer belt 421.
[0055] For example, two toner concentration detectors 43 are
disposed so as to face the respective end portions of intermediate
transfer belt 421 in the width direction thereof (that is, in the
direction orthogonal to the rotational direction of intermediate
transfer belt 421, or the horizontal scanning direction). Toner
concentration detector 43 is used to generate tone correction data.
The process for generating the tone correction data is performed,
for example, when a power source switch is turned on, every time
when a predetermined number of sheets are printed, when the
environmental variation around the apparatus (temperature,
humidity, etc.) exceeds a predetermined range, when the apparatus
is restarted after troubles such as malfunction are cleared, and
when an image stabilization control for stably creating an output
image from an input image is being executed. Toner concentration
detector 43 detects the concentration of a patch image which is
used for the tone correction and formed in a non-image formation
region (both end portions of intermediate transfer belt 421 in the
width direction) of intermediate transfer belt 421 in such a manner
as to face toner concentration detector 43 when intermediate
transfer belt 421 rotates. Toner concentration detector 43 outputs
a detected concentration to control section 70. The patch image has
a size of 20 [mm] (horizontal scanning direction).times.18 [mm]
(vertical scanning direction), for example.
[0056] Toner concentration detector 43 may be a photodetector of a
reflection type that includes a light emitting device such as
light-emitting diode (LED) and a photodetector such as photodiode
(PD), and detects the toner adhesion amount (concentration) of the
patch image, for example. A toner adhesion amount of a patch image
is represented as -log (I/I0) wherein I0 is the amount of light
incident on the patch image, and I is the amount of light reflected
from the patch image. As is obvious from the expression, as the
toner adhesion amount of the patch image formed on intermediate
transfer belt 421 increases, the amount of light received by the
photodetector decreases and accordingly the light reflection amount
I decreases, and consequently, the detector output value output
from toner concentration detector 43 decreases. Conversely, as the
toner adhesion amount of the patch image formed on intermediate
transfer belt 421 decreases, the amount of light received by the
photodetector increases and accordingly the light reflection amount
I increases, and consequently, the detector output value output
from toner concentration detector 43 increases.
[0057] It is to be noted that the position where toner
concentration detector 43 is disposed is not limited to the
above-described position. For example, toner concentration detector
43 may be disposed on the upstream side in the rotational direction
of intermediate transfer belt 421 relative to the secondary
transfer position. It suffices that toner concentration detector 43
is so disposed that toner concentration detector 43 can detect the
toner adhesion amount of a patch image formed on intermediate
transfer belt 421. In addition, in the case where intermediate
transfer belt 421 is made of a light transmissive material, it is
possible to adopt as toner concentration detector 43 a
photodetector of a transmission type in which a light emitting
device and a photodetector are disposed in facing relation with
intermediate transfer belt 421 therebetween.
[0058] Fixing section 60 is of a belt heating type. Fixing section
60 includes an upper pressing section and a lower pressing section
which form a fixing nip portion. Upper pressing section includes a
heating roller and a fixing roller. Across the heating roller and
the fixing roller, an endless fixing belt is installed with a
predetermined belt tensile force. The lower pressing section
includes a pressure roller. The pressure roller is brought into
pressure contact with the fixing roller with a predetermined fixing
load with the fixing belt therebetween. Thus, the fixing nip
portion for conveying recording sheet S in a tightly sandwiching
manner is formed between the fixing roller and the pressure roller.
Fixing section 60 applies heat and pressure to recording sheet S
conveyed thereto at the fixing nip portion, thereby fixing a toner
image to recording sheet S. It is to be noted that fixing section
60 may be of a roller heating type, or may be a non-contact type
fixing member that uses a heat source such as a heating lamp and a
heater to heat recording sheet S in a non-contact manner.
[0059] Sheet conveying section 50 includes sheet feeding section
51, sheet ejection section 52, and sheet ejection section 53. Three
sheet feed tray units 51a to 51c included in sheet feeding section
51 store sheets S (for example, standard sheets or special sheets)
discriminated on the basis of the basis weight, the size, and the
like, for each type set in advance.
[0060] Sheets S stored in sheet feed tray units 51a to 51c are send
out one by one from the topmost sheet, and are conveyed to image
forming section 40 by conveying mechanism 52 having a plurality of
conveyance rollers including registration roller 52a and the like.
At this time, a registration roller section provided with
registration rollers 52a corrects skew of sheet S fed thereto, and
adjusts conveyance timing. Then, image forming section 40
collectively secondary-transfers the toner images on intermediate
transfer belt 421 to the surface of recording sheet S, and fixing
section 60 performs a fixing process thereon. Recording sheet S on
which an image has been formed is ejected out of image forming
apparatus 1 by sheet ejection section 53 including ejection rollers
53a.
[0061] Next, the detailed configuration of developing device 412
will be described.
[Configuration of Developing Device 412]
[0062] As illustrated in FIG. 3, developing device 412 includes
housing 101 (developer housing section) that houses a developer.
Housing 101 is partitioned by wall 102 into stirring chamber 103
and supply chamber 104, and a developer including toner and carrier
is housed in housing 101. Stirring screw 105, which is disposed
inside stirring chamber 103, conveys the toner and carrier toward
the left side in FIG. 3 while stirring the toner and carrier to
thereby triboelectrically charge the toner. Supplying screw 106 is
disposed inside supply chamber 104, and configured to supply the
developer containing the charged toner to developing roller 108
while conveying the developer toward the right side in FIG. 3.
[0063] In developing roller 108, a sleeve roller rotates around a
fixedly disposed magnet roller, and supplying screw 106 supplies a
developer to the outer peripheral surface of the sleeve roller.
When the developer supplied to the outer peripheral surface of the
sleeve roller moves on the outer peripheral surface of the sleeve
roller, the carrier forms a magnetic brush by the magnetic force of
magnetic poles provided to the magnet roller. The toner adhered to
the magnetic brush adheres to an electrostatic latent image on
photoconductor drum 413. Thus, the electrostatic latent image of
photoconductor drum 413 is developed by the toner.
[0064] The magnet roller has five magnetic poles N1, S1, N2, N3,
and S2 provided along the rotational direction of the sleeve
roller. Among these magnetic poles, main magnetic pole N1 is
disposed at a position facing photoconductor drum 413. Same pole
sections N2 and N3 that generate repulsive magnetic field for
separating the developer on the sleeve roller are disposed at
respective positions facing the inside of developing device 412.
The rotational direction of the sleeve roller is the same as that
of photoconductor drum 413 (that is, at a position where the sleeve
roller and photoconductor drum 413 face each other, the rotational
directions of the sleeve roller and photoconductor drum 413 are
opposite to each other).
[0065] Supplying screw 106 and stirring screw 105 are spiral screws
respectively provided with spiral vanes 110 and 112. Each of spiral
vanes 110 and 112 has a predetermined spiral pitch and is provided
over the substantially entire region of the shaft (rotational
axis). Developing roller 108, supplying screw 106, and stirring
screw 105 are disposed in such a manner that developing roller 108,
the rotational axes of supplying screw 106, and stirring screw 105
are in parallel to each other.
[0066] On both end sides of partition wall 102, communication ports
114 and 116 for exchanging the developer between stirring chamber
103 and supply chamber 104 are provided, thus forming a circulation
path in which the developer housed in housing 101 circulates
between stirring chamber 103 and supply chamber 104 through
communication ports 114 and 116 while being stirred by stirring
screw 105 and supplying screw 106. It is to be noted that the
circulation path formed inside housing 101 may be a vertical
circulation path, or a three-axis circulation path.
[0067] Carrier replenishment port 118 is provided on the upstream
side of stirring chamber 103 in the developer conveyance direction.
At carrier replenishment port 118 (carrier replenishment position),
supply of carrier is received through carrier hopper 120 (carrier
replenishing section) filled with carrier.
[0068] At a portion near carrier replenishment port 118, carrier
concentration detector 140 (carrier concentration detecting
section) that detects the carrier concentration (the ratio of the
carrier in the developer) in housing 101 is provided. The carrier
concentration detector 140, which is also called TCR detector,
outputs a detected carrier concentration to control section 70. For
example, carrier concentration detector 140 outputs a detector
signal containing a count value which is in substantially inverse
proportion to the value of the carrier concentration. Control
section 70 can determine the value of the carrier concentration on
the basis of the count value contained in the detector signal
output from carrier concentration detector 140.
[0069] The portion near carrier replenishment port 118 corresponds
to a range of the position of carrier concentration detector 140
within which change in carrier concentration can be detected before
the carrier is completely mixed with the developer in housing 101
when carrier is supplied through carrier hopper 120. In the present
embodiment, carrier concentration detector 140 is disposed on the
bottom surface of stirring chamber 103 and on the downstream side
of carrier replenishment port 118 in the developer conveyance
direction of stirring chamber 103.
[0070] Carrier concentration detector 140 is a magnetic detector
that measures change in magnetic permeability of the developer by
utilizing the fact that carrier is a paramagnetic substance to
detect the carrier concentration on the basis of the amount of
carrier in a unit volume. Carrier concentration detector 140
detects change in inductance of two coils caused by change in
magnetic permeability as the carrier concentration. It is to be
noted that carrier concentration detector 140 is not limited to
magnetic detectors, and reflection type photodetectors may be
adopted as carrier concentration detector 140, similarly to toner
concentration detector 43.
[0071] Toner replenishment port 122 is provided on the upstream
side of carrier replenishment port 118 in the developer conveyance
direction of stirring chamber 103. At toner replenishment port 122,
supply of toner is received through toner hopper 124 filled with
toner.
[0072] It is also possible to adopt a configuration in which
carrier hopper 120 is filled with toner together with carrier and
the toner and carrier are separately supplied. In addition, carrier
hopper 120 may supply carrier to developing device 412 of each of
image forming units 41Y, 41M, 41C and 41K. In addition, it is also
possible to adopt a configuration in which toner hopper 124 is
filled with carrier together with toner and the toner and carrier
are separately supplied.
[0073] The shaft of supplying screw 106 extends toward the
downstream side in the developer conveyance direction beyond
communication port 116, and the end portion of the shaft on the
downstream side in the developer conveyance direction is located in
developer ejection section 126 protruding toward the downstream
side in the developer conveyance direction of supply chamber
104.
[0074] The shaft of supplying screw 106 is provided with, on its
downstream side in the developer conveyance direction, reverse
spiral vane 128 whose spiral direction is opposite to that of
spiral vane 110. Reverse spiral vane 128 has a spiral pitch smaller
than that of spiral vane 110. Reverse spiral vane 128 controls
conveyance of the developer in the developer conveyance direction
of supplying screw 106 so as to forward the developer to
communication port 116.
[0075] The shaft of supplying screw 106 located in developer
ejection section 126 is provided with spiral vane 130 whose spiral
direction is the same as that of spiral vane 110. Spiral vane 130
has a spiral pitch smaller than that of spiral vane 110.
[0076] Developer discharge port 132 for discharging the developer
is provided on the bottom surface of developer ejection section
126. Spiral vane 130 forwards the developer which has passed
through reverse spiral vane 128 to developer discharge port 132.
Developer correction container 134 is mounted to developer
discharge port 132. As in the present embodiment, developer
discharge port 132 is desirably provided at a position where the
supplied carrier is sufficiently mixed with the developer in
housing 101 (the most downstream position in the developer
conveyance direction) so that the supplied toner is not discharged
instantly.
[0077] Reverse spiral vane 128 and spiral vane 130 of supplying
screw 106 and developer ejection section 126 form a trickle
discharging mechanism for discharging excess developer from
developer discharge port 132 when the amount of the developer in
housing 101 is excessively increased. It is to be noted that the
developer discharging mechanism may have a configuration in which
the height of housing 101 is so set that only developer discharge
port 132 is low for the purpose of discharging excess developer in
housing 101 from developer discharge port 132.
[0078] Next, a toner replenishment control operation will be
described with reference to the flowchart of FIG. 4.
[Toner Replenishment Control Operation]
[0079] First, image reading section 10 generates input image data
on the basis of a result of reading by document image scanning
device 12 (step S100). Next, image processing section 30 performs
various digital image processing on the input image data generated
by image reading section 10, and outputs an image signal subjected
to the image processing as output image information (step
S120).
[0080] Next, control section 70 computes an toner consumption
amount required for an image forming process performed by image
forming section 40 on the basis of output image information output
from image processing section 30 (step S140). Finally, in
accordance with the toner consumption amount thus computed, control
section 70 outputs, to toner hopper 124, a toner replenishment
control signal requesting supply of toner (step S160). As a result,
toner is supplied from toner hopper 124 to toner replenishment port
122. Upon completion of the process of step S160, the toner
replenishment control operation is terminated. It is to be noted
that, in the present embodiment, control section 70 computes the
consumption amount of the color toners of the Y-component,
M-component, C-component and K-component on the basis of the output
image information, and controls developing device 412 to supply
toner corresponding to the consumption amount thus computed.
[0081] Next, an operation for checking toner replenishment will be
described with reference to the flowchart of FIG. 5. The checking
operation is executed after the replenishment operation is
performed.
[Operation for Checking Toner Replenishment]
[0082] In the following, an example will be described in which
image forming section 40 is controlled to form a patch image of the
toner of the K-component on intermediate transfer belt 421.
[0083] First, control section 70 controls image forming section 40
to form a patch image of the toner of the K-component on
intermediate transfer belt 421 (step S200). Next, control section
70 indirectly obtains the toner concentration of the patch image on
intermediate transfer belt 421 which is detected by toner
concentration detector 43, as the toner concentration in housing
101 (step S220). The toner concentration thus obtained is
temporarily stored in RAM 73. After passing through a detecting
region of toner concentration detector 43, the patch image formed
on intermediate transfer belt 421 is removed by belt cleaning
device 426.
[0084] Next, control section 70 determines whether the toner
concentration of the patch image obtained at step S220 is not lower
than a predetermined toner concentration (acceptable lower limit of
toner concentration) (step S240). When it is determined that the
toner concentration is not lower than the predetermined toner
concentration (YES at step S240), control section 70 determines
that the toner replenishment operation has been properly performed.
Then, the operation for checking the toner replenishment is
terminated.
[0085] On the other hand, when it is determined that the toner
concentration is lower than the predetermined toner concentration
(NO at step S240), control section 70 determines that the toner
replenishment operation has not been properly performed, and
controls display section 21 to display messages (toner
replenishment error) indicating necessity for measures such as
reconditioning of the toner replenishment mechanism, and
replacement of a toner bottle (not illustrated) which is provided
above toner hopper 124 and configured to supply toner to toner
hopper 124 (step S260). Upon completion of the process of step
S260, the operation for checking the toner replenishment is
terminated. It is to be noted that control section 70 may output
audio information indicating the toner replenishment error from a
speaker (not illustrated).
[0086] Next, a carrier replenishment control operation will be
described with reference to the flowchart of FIG. 6.
[Carrier Replenishment Control Operation]
[0087] In the following, an example will be described in which
carrier is supplied in an replenishment amount corresponding to the
driving time of developing device 412, but it is also possible to
supply carrier in an replenishment amount corresponding to the
number of printed sheets.
[0088] First, control section 70 obtains the driving time of
developing device 412 (step S300). Next, control section 70
determines whether the obtained driving time is not shorter than a
first predetermined time period (for example, 10 [min]) (step
S320). When it is determined that the driving time is shorter than
the first predetermined time period (NO at step S320), the process
is returned to step S300.
[0089] On the other hand, when it is determined that the driving
time is not shorter than the first predetermined time period (YES
at step S320), control section 70 outputs a carrier replenishment
control signal requesting supply of carrier in accordance with the
obtained driving time to carrier hopper 120 (step S340). As a
result, a carrier replenishment operation from carrier hopper 120
to carrier replenishment port 118 is started.
[0090] Next, control section 70 activates a timer not illustrated
(step S360). Next, whether a time measured by the timer activated
by control section 70 (hereinafter referred to as timer time) is
not shorter than a second predetermined time period (for example,
two [seconds]) is determined (step S380). When it is determined
that the timer time is shorter than the second predetermined time
period (NO at step S380), the process is returned to step S380.
[0091] On the other hand, when it is determined that the timer time
is not shorter than the second predetermined time period (YES at
step S380), control section 70 obtains the carrier concentration
detected by carrier concentration detector 140 during the second
predetermined time period (step S400). It is to be noted that
control section 70 deactivates the timer. Next, control section 70
determines whether the carrier concentration obtained at step S400
is higher than a predetermined carrier concentration (step S420).
When it is determined that the carrier concentration is higher than
the predetermined carrier concentration (YES at step S420), control
section 70 determines that the carrier replenishment operation has
been properly performed. Then, the carrier replenishment control
operation is terminated.
[0092] On the other hand, when it is determined that the carrier
concentration is not higher than the predetermined carrier
concentration (NO at step S420), control section 70 determines that
the carrier replenishment operation has not been properly
performed, and controls display section 21 to display messages
(carrier replenishment error) indicating necessity for measures
such as reconditioning of the carrier replenishment mechanism, and
replacement of a carrier bottle (not illustrated) which is provided
above carrier hopper 120 and configured to supply carrier to
carrier hopper 120 (step S440). Upon completion of the process of
step S440, the operation for checking the carrier replenishment is
terminated. It is to be noted that control section 70 may output
audio information indicating the carrier replenishment error from a
speaker (not illustrated).
[0093] FIG. 7 illustrates a varying state of the carrier
concentration detected by carrier concentration detector 140 in a
carrier replenishment control operation. In FIG. 7, the abscissa
represents time, and the ordinate represents the carrier
concentration. Here, an exemplary case is described in which a
replenishment control operation for supplying 1 [g] carrier is
performed in a state where housing 101 of developing device 412 is
filled with 800 [g] developer. Time T1 is a time at which a carrier
replenishment control signal is output to carrier hopper 120, and a
replenishment operation for supplying carrier to carrier
replenishment port 118 is started. Time T2 is a time at which the
supplied carrier reaches the detecting region of carrier
concentration detector 140, and starts to pass through the
detecting region. Time T3 is a time at which the supplied carrier
exits the detecting region of carrier concentration detector 140.
The period from time T1 to time T3 corresponds to the second
predetermined time period described in the flowchart of FIG. 6.
Times T2 and T3 can be acquired by a simulation on the basis of
conditions such as the structure of developing device 412 and the
position of carrier concentration detector 140.
[0094] In the present embodiment, control section 70 obtains the
carrier concentration (represented by curve L2) detected by carrier
concentration detector 140 in the period from time T1 to time T3.
Then, when the carrier concentration detected in the period from
time T2 to time T3 is not lower than a threshold level
(predetermined carrier concentration) represented by dotted line L1
as illustrated in FIG. 7, control section 70 determines that the
carrier replenishment operation has been properly performed.
[0095] FIG. 8 illustrates a configuration of developing device 412
in the case where carrier concentration detector 140 is provided at
a position distanced from carrier replenishment port 118. In this
configuration, carrier replenishment port 118 is provided at a
position near toner replenishment port 122 on the downstream side
in the developer conveyance direction of stirring chamber 103.
[0096] FIG. 9 illustrates a varying state of the carrier
concentration detected by carrier concentration detector 140 when a
carrier replenishment control operation is performed in developing
device 412 of FIG. 8. In FIG. 9, the abscissa represents time, and
the ordinate represents the carrier concentration. Here, an
exemplary case is described in which a replenishment control
operation for supplying 1 [g] carrier is performed in a state where
housing 101 of developing device 412 is filled with 800 [g]
developer.
[0097] Time T1 is a time at which a carrier replenishment control
signal is output to carrier hopper 120, and a replenishment
operation for supplying carrier to carrier replenishment port 118
is started. Time T2 is a time at which the supplied carrier reaches
the detecting region of carrier concentration detector 140, and
starts to pass through the detecting region. Since the distance
between carrier replenishment port 118 and carrier concentration
detector 140 in developing device 412 of FIG. 8 is greater than
that of developing device 412 of FIG. 3, the period from time T1 to
time T2 is extended. Time T3 is a time at which the supplied
carrier exits the detecting region of carrier concentration
detector 140. The period from time T1 to time T3 corresponds to the
second predetermined time period described in the flowchart of FIG.
6. Times T2 and T3 can be acquired by a simulation on the basis of
conditions such as the structure of developing device 412 and the
position of carrier concentration detector 140.
[0098] Control section 70 obtains the carrier concentration
(represented by curve L3) detected by carrier concentration
detector 140 in the period from time T1 to time T3. Then, when the
carrier concentration detected in the period from time T2 to time
T3 is lower than a threshold level represented by dotted line L1
(predetermined carrier concentration) as illustrated in FIG. 9,
control section 70 determines that the carrier replenishment
operation has not been properly performed. As described, when the
distance between carrier replenishment port 118 and carrier
concentration detector 140 is great, carrier concentration detector
140 cannot detect the supplied carrier as a change in the carrier
concentration. Since the replenishment amount of carrier is as
small as 1.0 [g], the amount of increase in carrier concentration
after the carrier is sufficiently mixed with the developer housed
in housing 101 is estimated to be about 0.1[%]. The about 0.1 [%]
increase is not sufficient to determine whether the carrier
replenishment operation has been properly performed by using
carrier concentration detector 140.
Effect of the Present Embodiment
[0099] As has been described in detail, the developing device
according to the present embodiment includes: housing 101
configured to house a developer including toner and carrier;
carrier hopper 120 configured to supply the carrier to housing 101;
carrier concentration detector 140 provided at a position near
carrier replenishment port 118 at which the carrier is received
from carrier hopper 120 in housing 101, carrier concentration
detector 140 being configured to detect a carrier concentration in
housing 101; and control section 70 configured to determine whether
the carrier is properly supplied to housing 101 on the basis of a
result of detecting by carrier concentration detector 140. To be
more specific, control section 70 determines that the carrier has
been properly supplied to housing 101 when the carrier
concentration detected by carrier concentration detector 140 is not
lower than a predetermined concentration, and determines that the
carrier has not been properly supplied to housing 101 when the
carrier concentration detected by carrier concentration detector
140 is lower than a predetermined concentration.
[0100] Carrier is very easily mixed with a developer as compared
with toner. In particular, carrier is instantly mixed with a
developer when a small amount of carrier is supplied. According to
the embodiment, however, change in the carrier concentration can be
detected before carrier is completely mixed with a developer at the
time of the carrier replenishment control operation, and therefore
whether supply of carrier has been properly performed can be
accurately determined. Consequently, when supply of carrier has not
been properly performed, it is possible to notify the user of such
a fact so as to take measures such as reconditioning of the carrier
replenishment mechanism, and replacement of a carrier bottle. As a
result, a situation where the replacement of degraded carrier with
newly supplied carrier is not performed for a long period can be
prevented, and favorable toner charging performance can be
maintained for a long period, whereby favorable images without
fogging, toner scattering, and the like can be formed. In the
above-mentioned manner, it is possible to prevent a defect which is
caused when supply of carrier is not properly performed in the case
where toner and carrier are separately supplied.
MODIFICATION
[0101] While in the above-mentioned embodiment an example is
described in which whether carrier has been properly supplied to
housing 101 is determined on the basis of a result detected by one
carrier concentration detector 140, the present invention is not
limited thereto. For example, whether carrier has been properly
supplied to housing 101 can be determined on the basis of results
detected by two carrier concentration detectors 140. In this case,
two carrier concentration detectors 140 are respectively provided
at a position near carrier replenishment port 118 and a position
distanced from carrier replenishment port 118. Control section 70
determines that carrier has been properly supplied to housing 101
when the difference between the carrier concentrations detected by
two carrier concentration detectors 140 is not lower than a
predetermined concentration, and determines that carrier has not
been properly supplied to housing 101 when the difference between
the carrier concentrations detected by two carrier concentration
detectors 140 is lower than the predetermined concentration.
[0102] In addition, in the above-mentioned embodiment, carrier
concentration detector 140 may function as a member that directly
detects the toner concentration in housing 101. With this
configuration, provision of toner concentration detector 43, and
forming of a patch image on intermediate transfer belt 421 are not
required, and the toner concentration in housing 101 can be
accurately detected. In this case, desirably, a toner concentration
in a steady state, which is established after toner supplied from
toner hopper 124 is sufficiently stirred and mixed with the
developer in housing 101, can be detected, and carrier
concentration detector 140 is distanced from toner replenishment
port 122 as much as possible. For example, desirably, carrier
concentration detector 140 is provided at a position on the
upstream side of toner replenishment port 122 in the developer
conveyance direction, or a position separated from toner
replenishment port 122 by a predetermined distance on the
downstream side of toner replenishment port 122 in the developer
conveyance direction.
[0103] Incidentally, in the case where the toner replenishment
control operation is performed on the basis of the toner
concentration detected by carrier concentration detector 140 (that
is, in the case where toner is supplied when the toner
concentration is lower than a predetermined value), when the change
in the carrier concentration (that is, the change in the toner
concentration) as illustrated in FIG. 7 is detected at the time of
supply of carrier, control section 70 may determine that the toner
concentration in housing 101 is decreased, and may excessively
supply toner. Therefore, desirably, the toner replenishment control
operation using the toner concentration detected by carrier
concentration detector 140 is not performed in a third
predetermined time period (for example, 0.4 [seconds]) from a time
when carrier supplied from carrier hopper 120 reaches and starts to
pass through the detecting region of carrier concentration detector
140 until the carrier exits the detecting region. In other words,
it is desirable to determine whether carrier has been properly
supplied to housing 101 by using the carrier concentration detected
by carrier concentration detector 140 only in the third
predetermined time period.
[0104] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alterations may occur depending on design requirements and other
factors in so far as they are within the scope of the appended
claims or the equivalents thereof
* * * * *